Phylum – Arthropoda and Phylum – Mollusca

Phylum – Arthropoda:

· This is the largest phylum of Animalia which includes insects.

· Over two-thirds of all named species on earth are arthropods.

· They have organ-system level of organisation.

· They are bilaterally symmetrical, triploblastic, segmented and coelomate animals.

· The body of arthropods is covered by chitinous exoskeleton.

· The body consists of head, thorax and abdomen. They have jointed appendages (arthros-joint, poda-appendages).

· Respiratory organs are gills, book gills, book lungs or tracheal system.

· Circulatory system is of open type. Sensory organs like antennae, eyes (compound and simple), statocysts or balance organs are present.

· They are mostly dioecious. Fertilisation is usually internal. They are mostly oviparous. Development may be direct or indirect.

· Examples: Economically important insects – Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect) Vectors – Anopheles, Culex and Aedes (Mosquitoes) Gregarious pest – Locusta (Locust) Living fossil – Limulus (King crab).

Examples of Arthropoda : (a) Locust (b) Butterfly (c) Scorpion (d) Prawn

Phylum – Mollusca:

· This is the second largest animal phylum.

· Molluscs are terrestrial or aquatic (marine or fresh water) having an organ-system level of organisation.

· They are bilaterally symmetrical, triploblastic and coelomate animals.

· Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump.

· A soft and spongy layer of skin forms a mantle over the visceral hump.

· The space between the hump and the mantle is called the mantle cavity in which feather like gills are present.

· They have respiratory and excretory functions.

· The anterior head region has sensory tentacles.

· The mouth contains a file-like rasping organ for feeding, called radula.

· They are usually dioecious and oviparous with indirect development.

· Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Seahare), Dentalium (Tusk shell) and Chaetopleura (Chiton).

Examples of Mollusca : (a) Pila (b) Octopus